1986 GMC Jimmy Engine Overheats after Rebuils

Hello --

I had a new / rebuilt Chevy 350 engine put in my son's 1986 GMC Jimmy full size. First off -- there is no disptick. We were driving to Denver and noticed that the oil pressure gauge was at zero and the temp was up to like 180 degrees. Went to Jiffy Lube and they said there were just 3 quarts of oil in the car. They changed the oil with 5 quarts at this point the engine only has like 200 miles on it. Now the oil pressure gauge goes up under heavy acceleration but otherwise still sits at zero. Worse, the engine rocketed from 180 degrees to 260 degrees and overheated. Wont stay much below 200 degrees now when at highway speeds.